Field of the Invention
The present invention relates to an improvement of a differential device, particularly the differential device which includes a differential case; and a differential mechanism housed in the differential case and distributively transmitting rotational force of the differential case to a pair of mutually-independent output shafts.
Description of the Related Art
As such a differential device, Japanese Patent No. 5509910, for example, has made known a differential device in which, for example, a differential case includes: an input member having an input part that receives rotational force and formed in a cylindrical shape, an end portion of the input member on at least one side in an axial direction thereof being opened; and at least one cover portion covering the opened end portion of the input member on the one side in the axial direction. In this conventional device, an inner peripheral portion of a driven gear as the input part and an outer peripheral portion of the differential case are integrally joined together by a combination use of press-fitting means and welding means.
In joining the input part and the differential case together by a combination use of the press-fitting means and the welding means as in the conventional device, thermal strain occurs around welded portions during the welding, and also mechanical strain occurs around press-fitted portions during the press-fitting. Due to influences of the thermal strain and the mechanical strain, assembling precision of the input part and the differential case and accordingly the differential device as a whole may decrease.
In the above conventional device, the input part of the differential device in a certain layout or form, for example, in the form of a helical gear may cause thrust load from the input part side to act on the differential case to no small extent. In this case, stress tends to be concentrated on the welded portions which are boundary portions between the input part and the differential case, so that there is also a possibility of deterioration in durability of the welded portions, or the like.
Meanwhile, the same problems as described above occur also in a case of a combination use of the press-fitting means and the welding means to assemble constituent parts of the differential case, namely, a cylinder-shaped input member and cover portions covering open end portions of the input member.